Chứng tỏ rằng: 1/41 + 1/42 + 1/43 + 1/44 +...+ 1/60 > 1/3
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Chứng tỏ rằng: 1/41 + 1/42 + 1/43 + 1/44 +...+ 1 60 > 1 3
Chứng tỏ rằng:
1/41+1/42+1/43+1/44....+1/59+1/60>17/45
Chứng Tỏ rằng
1/41 +1/42+1/43+1/44+...+1/80<5/6
Ta có: \(\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+...+\frac{1}{60}< \frac{1}{40}+\frac{1}{40}+...+\frac{1}{40}=\frac{1}{40}.20=\frac{1}{2}\)
\(\frac{1}{61}+\frac{1}{62}+\frac{1}{63}+...+\frac{1}{80}< \frac{1}{60}+\frac{1}{60}+\frac{1}{60}+...+\frac{1}{60}=\frac{1}{60}.20=\frac{1}{3}\)
\(\Rightarrow\frac{1}{41}+\frac{1}{42}+...+\frac{1}{80}< \frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=\frac{3+2}{6}=\frac{5}{6}\) (đpcm)
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Chứng tỏ rằng : 7/12 <1/41 +1/42 + 1/43 + 1/44 + ..... +1/79 +1/80 <1
hãy chứng tỏ rằng : 1/41 + 1/42 + 1/43 + ... + 1/80 > 3/5
Hãy chứng tỏ rằng:
a) 1/41+1/42+1/43+...+1/79+1/80>7/12
b)11/15<1/21+1/22+1/23+...+1/59+1/60<3/2
Chứng tỏ rằng: 1/41+1/42+1/43+...+1/79+1/80>7/12
chứng tỏ rằng :1 /41 +1/42 +1/43 +...+1/79+1/80 >7/12
Ta có:
7/12 = 4/12 + 3/12 = 1/3 + 1/4 = 20/60 + 20/80
1/41 + 1/42 + 1/43 +...+ 1/79 + 1/80 = (1/41 + 1/42 + 1/43 + ...+ 1/60) + (1/61 + 1/62 +...+ 1/79 + 1/80)
Do 1/41> 1/42 > 1/43 > ...>1/59 > 1/60
=> (1/41 + 1/42 + 1/43 + ...+ 1/60) > 1/60 + ...+ 1/60 = 20/60
và 1/61> 1/62> ... >1/79> 1/80
=> (1/61 + 1/62 +...+ 1/79 + 1/80) > 1/80 + ...+ 1/80 = 20/80
Vậy: 1/41 + 1/42 + 1/43 +...+ 1/79 + 1/80 > 20/60 + 20/80 = 7/12
=> 1/41 + 1/42 + 1/43 +...+ 1/79 + 1/80 > 7/12
=> ĐPCM
tk nha mk trả lời đầu tiên đó!!!
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chứng tỏ rằng :1/41+1/42+1/43+........+2/80>17/12